An ozone generating device which generates ozone (O3) by using discharge will be described. Ozone is utilized as a strong oxidizing agent in a wide variety of fields including an aqueous environment purification technology such as water and sewage treatment, etc., a sterilization technology and a semiconductor cleaning technology, etc. Corresponding to recent growing environmental awareness and increase in demand for electronic devices, demand for technology regarding ozone generation with high concentration and high efficiency is increased.
As a discharge method for generating ozone, mainly a silent discharge method is used. In a silent discharge type ozone generating device, by using discharge, oxygen molecules are dissociated for generating ozone, and in order to enhance an ozone concentration and an efficiency of a silent discharge type ozone generating devices, in every country in the word, research and development has been advanced. In actual ozone generating devices, approximately 10% of input electric power is transformed to be ozone, and remaining 90% of input electric power is transformed to thermal energy in a discharge space. Here, when the thermal energy causes a discharge space to be a high temperature, ozone which is generated is decreased through the thermal decomposition reaction, consequently, the thermal decomposition reaction is one of factors to suppress to enhance an ozone concentration and high efficiency of an ozone generating device. That is, by making a temperature of a discharge space to be low, thermal decomposition of ozone is suppressed, therefore, ozone generating efficiency is improved and high concentration ozone can be generated. Here, the ozone generating efficiency designates ozone weight which can be generated per unit discharge electric power. In conventional ozone generating devices, generally, by using water which is stored in a tank such as a cooling tower, etc. or tap water (hereinafter, will be referred as normal temperature water), electrodes are cooled so as to make a discharge space to be a low temperature. In some cases, electrodes are cooled by directly contacting normal temperature water, and in other cases, cooling water at a side of an ozone generating device is circulated in a closed path, by heat exchange between the normal temperature water, a temperature of the cooling water is maintained. In either case, a temperature of the normal temperature water is approximately 25 degrees Celsius, and it is found such that by using water whose temperature is lower than 25 degrees Celsius, ozone can be generated more efficiently. Consequently, as a means to maintain a temperature of a refrigerant to be lower than normal temperature, a low temperature circulating device (hereinafter, will be referred as a chiller) is utilized. However, in a case where a chiller is used, electric power is also consumed for operating a chiller, therefore, there is a problem such that consumption electric power for whole of ozone generating system is increased.
As countermeasures for the above mentioned problems, a method for decreasing a temperature of a discharge space by utilizing cold heat of a liquefied raw material including liquid oxygen, liquid nitrogen, liquid carbon dioxide and liquid air as a raw material for an ozone generating device is disclosed. A method, in which a liquefied raw material which is liquid having an extremely low temperature is utilized as a refrigerant, cooling cost for cooling a refrigerant is not required, consequently, a discharge space can be efficiently cooled, is proposed. For example, a method in which a liquefied raw material is sprayed to a fin which is provided on an electrode so as to cool the electrode by using evaporation heat transfer (for example, Patent Document 1), a method in which after an ozone generating unit is cooled by introducing a liquid raw material to a body of an ozone generating device, the liquid raw material is utilized as a material gas (for example, Patent Document 2), and a method for decreasing a temperature in a discharge space by introducing a material gas, which has a low temperature and is immediately after evaporation, to an ozone generating unit (for example, Patent Document 3), etc. are proposed.